The present invention relates to a damper device for a two-wheeled vehicle and in particular for a bicycle, which bicycle may be equipped with an auxiliary drive. The damper device may for example serve as a rear wheel damper or be part of, or be configured as, a suspension fork.
Many different types of rear wheel dampers and suspension forks for bicycles have become known in the prior art. Typically a damping unit for a rear wheel of a bicycle comprises at least one spring for cushioning shocks, and a damper for damping spring vibrations.
Most dampers for bicycles are operated with a damping fluid such as oil. For damping, the damping fluid is conveyed from a first damping chamber to a second damping chamber through a valve gate throttling the flow. The size of the valve gate aperture determines the damping strength. For application in bicycles it is desirable to have a load-sensitive damping level regulation. Thus for example slight damping may be provided for weak shocks and stronger damping for heavy shocks.
An optimal damping is also dependent on the terrain characteristics. Thus, for rides over roads, on forest paths or off-road, different damping settings are optimal.
For adjusting and influencing damping, ferromagnetic fluids have become known whose characteristics can be influenced by means of applying a magnetic field. Ferromagnetic fluids tend to consist of a suspension of minuscule particles which can be magnetically polarized and which are finely dispersed in a carrier liquid. The polarizable particles tend to consist of carbonyl ferrous powder and their diameters are typically between 0.1 and 50 micrometers, forming chain-like structures under the influence of a magnetic field such that the ferromagnetic fluid viscosity will considerably rise under the influence of a magnetic field in particular perpendicular to the field lines of the magnetic field.
As the magnetic field is switched off, the viscosity will drop virtually instantaneously. Examinations have shown that the typical response time lies in the range of a few milliseconds or even less. Thus, ferromagnetic fluids are suitable to be used in dampers of bicycles.
With U.S. Pat. No. 6,471,018 B1, a ferromagnetic damper has become known in which an electromagnet exposes a flow passage between the first and the second damper chambers to a magnetic field to set the desired damping level. One advantage of such a damper is that the chain-forming of the ferromagnetic particles can be controlled through the magnetic field strength. Setting the strength of an electromagnet is simple such that a flexible system is provided. The drawback of the known system in particular when used in bicycles is, however, that the electromagnet needs to be supplied with electric energy at all times during operation to ensure the desired damping characteristics. The continuous power requirement is a drawback in particular when used in bicycles since in the case of commercially available batteries either the operating time will decrease or the extra weight of power supply will increase.
To reduce the electric energy required it has thus become known to employ a permanent magnet in combination with an electromagnet wherein the permanent magnet generates a desired basic magnetic field strength which is modulated by the electromagnet as desired. Thus, with a suitable circuit arrangement of the electromagnet the magnetic field acting in the ferromagnetic operating gap may intensify or else be attenuated while the electromagnet is in operation. This system, however, still continuously requires electric energy for each setting deviating from the normal settings such that the functional range of the bicycle is again limited. The more the selected operational point deviates from the normal settings fixedly specified by the permanent magnet, the more energy will be required.
What is aggravating when employed as a bicycle damper is that various damper operating modes having different requirements such as “lockout” or “weak platform” may prevail for long periods. “Lockout” designates the mechanism of a suspension fork blocking the damper, while “platform” is understood to mean various characteristic damper curves. A damper optimized by way of permanent magnets for low energy absorption in one specific operating mode (e.g. medium platform) inevitably consumes conspicuously more energy in other operational modes (e.g. lockout).